RandomizedSet

Author: idf

380 Insert Delete GetRandom O(1).py

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+"""
+Design a data structure that supports all following operations in average O(1) time.
+
+insert(val): Inserts an item val to the set if not already present.
+remove(val): Removes an item val from the set if present.
+getRandom: Returns a random element from current set of elements. Each element must have the same probability of
+being returned.
+Example:
+
+// Init an empty set.
+RandomizedSet randomSet = new RandomizedSet();
+
+// Inserts 1 to the set. Returns true as 1 was inserted successfully.
+randomSet.insert(1);
+
+// Returns false as 2 does not exist in the set.
+randomSet.remove(2);
+
+// Inserts 2 to the set, returns true. Set now contains [1,2].
+randomSet.insert(2);
+
+// getRandom should return either 1 or 2 randomly.
+randomSet.getRandom();
+
+// Removes 1 from the set, returns true. Set now contains [2].
+randomSet.remove(1);
+
+// 2 was already in the set, so return false.
+randomSet.insert(2);
+
+// Since 1 is the only number in the set, getRandom always return 1.
+randomSet.getRandom();
+"""
+import random
+
+__author__ = 'Daniel'
+
+
+class RandomizedSet(object):
+    def __init__(self):
+        """
+        1. Use List of numbers to support O(1) getRandom
+        2. need an efficient way to find and delete an element
+        3. Use Map to get the location, move to end and pop
+        Initialize your data structure here.
+        """
+        self.lst = []
+        self.pos = {}
+
+    def insert(self, val):
+        """
+        Inserts a value to the set. Returns true if the set did not already contain the specified element.
+        :type val: int
+        :rtype: bool
+        """
+        if val in self.pos:
+            return False
+
+        self.lst.append(val)
+        self.pos[val] = len(self.lst) - 1
+
+        return True
+
+    def remove(self, val):
+        """
+        Removes a value from the set. Returns true if the set contained the specified element.
+        :type val: int
+        :rtype: bool
+        """
+        if val not in self.pos:
+            return False
+
+        idx, last = self.pos[val], len(self.lst) - 1
+        self.lst[idx], self.lst[last] = self.lst[last], self.lst[idx]
+        self.pos[self.lst[idx]] = idx
+
+        del self.pos[val]
+        self.lst.pop()
+
+        return True
+
+    def getRandom(self):
+        """
+        Gets a random element from the set.
+        :rtype: int
+        """
+        return random.choice(self.lst)
+
+
+class RandomizedSetTLE(object):
+    def __init__(self):
+        """
+        Initialize your data structure here.
+        """
+        self.set = set()
+
+    def insert(self, val):
+        """
+        Inserts a value to the set. Returns true if the set did not already contain the specified element.
+        :type val: int
+        :rtype: bool
+        """
+        ret = val not in self.set
+        self.set.add(val)
+        return ret
+
+    def remove(self, val):
+        """
+        Removes a value from the set. Returns true if the set contained the specified element.
+        :type val: int
+        :rtype: bool
+        """
+        ret = val in self.set
+        self.set.discard(val)
+        return ret
+
+    def getRandom(self):
+        """
+        Get a random element from the set.
+        :rtype: int
+        """
+        return random.sample(self.set, 1)[0]  # O(N), equivalent to random.choice(tuple(allLetters))
+
+
+
+# Your RandomizedSet object will be instantiated and called as such:
+# obj = RandomizedSet()
+# param_1 = obj.insert(val)
+# param_2 = obj.remove(val)
+# param_3 = obj.getRandom()